The electronic configuration of an element is defined as follows: A stepwise distribution of electrons in different orbits (energy levels) of an atom is called its electronic configuration. To write the electric configuration of an element, one should proceed as follows.
Atoms only losing or gaining electrons give rise to electrically charged particles called ions. The positively charged ions are called cation, while the negatively charged ion is called anion.
The electronic configuration of an element gives an idea about its reactivity. The elements having a completely filled outermost orbit (or shell) will be chemically inert (non-reactive). For example, the outermost shell in the case of helium (He), neon (Ne) and argon (Ar) are completely filled as shown below.